Proteins of the nuclear envelope are differentially expressed in human cancer and development. Variations in their expression may underlie the phenotypic differences in nuclear morphology, gene expression and mitotic potential that occur in cancer and cell differentiation. Nuclear envelope proteins have clinical utility as tumor rnarkers, especially in the diagnosis of leukemias and small cell lung carcinomas which do not express two proteins of the nuclear lamina called lamin A and lamin C. As nuclear envelope proteins play a prominent role in the disassembly and reassembly of the nucleus that occur during rnitosis, they could be potential targets for therapeutic agents designed to control the rate of cell division. Studies on the nuclear envelope are therefore significant to the pathobiology of cancer. For this reason, the present proposal is designed to examine the functions of human nuclear envelope proteins and the regulation of their genes. In the first specific aim, the interactions of LBR, an integral protein of the inner nuclear membrane, with lamin B 1 and chromatin will be studied to better understand the process of nuclear envelope reassembly at the end of mitosis. Alterations in these interactions, induced by mitosis-specific phosphorylation by p34cdc2 protein kinase and subsequent dephosphorylation, are likely responsible for nuclear envelope breakdown and reassembly. The affects of phosphorylation on these interactions will therefore be examined using cell-free chromatin and protein binding assays. The second specific aim of the proposal will further address the functions of LBR in cell division and nuclear morphology. Antisense methods will be used to inhibit LBR expression and determine how the lack of this protein affects nuclear structure and the potential of cells to divide. The results will provide insights into the function of this inner nuclear membrane protein in vivo. The experiments in the third specific aim will focus on the nuclear lamins, intermediate filament proteins of the nuclear lamina Because lamins A and C, which arise from the same gene by altemative splicing, are differentially expressed in cancer and development, an analysis of the factors that regulate the expression of this gene will be performed. The human gene for lamin B 1, a constitutively expressed lamin protein, will be investigated as a control. The regulatory regions of these genes will be analyzed using cell transfection assays in which the promoters are attached to reporter genes. By inhibiting expression using antisense methods, it will also be determined how lamin A and/or lamin C function in cell differentiation. The results of the proposed studies will provide basic information about the nuclear envelope relevant to the pathobiology of cancer. They will lay the foundation for the development of methods to inhibit cell division and for future studies on the role of nuclear envelope proteins in cell differentiation and cancer.